A number of substituted benzimidazole compounds have been discovered that display unusually good antiviral activity, see for example U.S. Pat. Nos. 4,008,243; 4,018,790; 4,118,573; and 4,118,742. Among the most active of such benzimidazole antiviral agents are two oximes, which are the syn and anti isomers of 1-isopropylsulfonyl-2-amino-6-(.alpha.-hydroxyiminobenzyl)benzimidazole. These oximes are especially active against rhinoviruses that cause upper respiratory infections. The separation of the syn and anti oximes is described in U.S. Pat. No. 4,191,832.
Although the anti isomer of 1-isopropylsulfonyl-2-amino-6-(.alpha.-hydroxyiminobenzyl)benzimidazole is more potent than the syn isomer, the syn isomer is more bioavailable. Therefore, it is critical to have one isomer in essentially pure form depending upon the characteristic desired. It is an object of this invention to provide a method for converting a mixture of syn and anti isomer or pure anti isomer to the syn isomer using photolysis.